1. Field of the Invention
The present invention relates to a detection angle control method for laser sensors which are attached to industrial robots adapted for use in plants, production lines, etc. and are used to control paths of transfer of the robots.
2. Description of the Related Art
Conventionally known is a technique such that a robot is furnished with a laser sensor for sensing a region near the position of the robot on the advanced side thereof, the laser sensor is used to detect predetermined regions (ridge lines, weld lines, etc.) of an object of operation (hereinafter referred to as workpiece), and an instruction path for the robot is corrected in accordance with the result of detection of the laser sensor, whereby a robot path corresponding to a line of operation is obtained. For example, the position of the operation line is detected on each occasion by means of the laser sensor during operational program playback operation of the robot, and the instruction path is corrected on a real time basis according to the result of the detection as the robot is moved along a weld line. This system, called a real-time tracking system, is used for a robot for arc welding and the like.
Thus, according to an instruction path correction method using the laser sensor, the robot path can be settled corresponding to the position of each workpiece even in case the workpiece is not positioned accurately. Naturally, however, this can be attained only on the assumption that the workpiece position is normally detected by means of the laser sensor.
As mentioned later, the laser sensor deflectively scans the workpiece surface by projecting a laser beam thereon, and a reflection of the projected laser beam is detected by means of a light detector. Depending on the light reflecting properties (especially angular measure) of the workpiece surface, therefore, a satisfactory reflected light intensity cannot be obtained unless the attitude of the laser sensor for the detection of the workpiece position is selected properly.
In teaching a position to the robot furnished with the laser sensor by using a teaching playback system, a robot position (including an attitude) which is expected to provide an optimum laser sensor attitude for a standard workpiece position is taught under normal conditions.
In many cases, however, the positioning states of workpieces, as objects of operation, are subject to substantial variations during robot playback operation. It is difficult for the aforesaid teaching system, therefore, to keep the positions and attitudes of the individual workpieces and the laser sensor in good relations at all times. Even if there is an attitude which ensures maintenance of good relations with all the workpieces, moreover, detecting this attitude requires complicated adjusting operations, thus presenting a serious inconvenience.